Means for clamping on flexible printing plates

ABSTRACT

Means for clamping printing plates onto cylinders of offset printing presses. Two or more tandem-mounted clamping rail pairs each consisting of top and bottom clamping rails are mounted in the axial direction of the cylinders. The rails clamp the ends of the printing plate by means of clamping screws and tension the plate with the aid of tensioning screws. The rails are supported in relation to one another and at the cylinder end flanges by means of adjusting screws. In each case the top clamping rail of a clamping rail pair overlaps the bottom of clamping rail of the adjacent clamping rail pair. The overlapping clamping rail ends are clamped together by at least one clamping screw passed through slots.

United States Patent [1 1 Jeschke et al.

[451 Sept. 9, 1975 MEANS FOR CLAMPING ON FLEXIBLE PRINTING PLATES [75] Inventors: Willie Jeschke; Claus-Peter Zander,

both of Heidelberg, Germany [22] Filed: Feb. 13, 1974 [21] Appl. No.: 442,133

3,658,002 4/1972 Preuss 10l/415.l

FOREIGN PATENTS OR APPLICATIONS 1,231,259 12/1966 Germany l()l/4l5.l

Primary ExaminerEdgar S. Burr Assistant Examiner-Paul J. Hirsch Attorney, Agent, or Firm-Herbert L. Lerner [5 7 ABSTRACT Means for clamping printing plates onto cylinders of offset printing presses. Two or more tandem-mounted clamping rail pairs each consisting of top and bottom clamping rails are mounted in the axial direction of the cylinders. The rails clamp the ends of the printing plate by means of clamping screws and tension the plate with the aid of tensioning screws. The rails are supported in relation to one another and at the cylinder end flanges by means of adjusting screws. In each case the top clamping rail of a clamping rail pair overlaps the bottom of clamping rail of the adjacent clamping rail pair. The overlapping clamping rail ends are clamped together by at least one clamping screw passed through slots.

2 Claims, 3 Drawing Figures PATENTED SEP I975 sum 1 OF 2 MEANS FOR CLAMPING ON FLEXIBLE PRINTING PLATES The invention relates to means for clamping flexible printing plates onto cylinders of offset printing presses.

Two or more pairs of clamping rails are provided, consisting in each case of top and bottom clamping rails, located behind one another in axial direction of the cylinders. These pairs of clamping rails clamp the end of the printing plate by means of clamping screws and tension it with the aid of tensioning screws and are supported in relation to one another and onthe cylinder end flanges by means of adjusting screws.

In German patent specification No. l,23l,259, two pairs of clamping rails are provided at the tail end of the printing plate, these being adjustable in the axial direction of the cylinder by means of adjusting screws. 1n the case of multicolor printing it is a generally known process to remedy register inaccuracies of consecutive, different colored impression by deforming the rear end of the printing plate. This deformation is caused by altering the spacing of the pairs of clamping rails in relation to one another with the aid of adjusting screws. This deformation, taking the form of extension or compression, can only however take place in the section of the printing plate between the clampingrails which is not held by the two pairs of clamping railsv On account of the necessary, proper tension of the printing plate the extension or compression section must, however, be kept very small. The result is that because of overload the printing plate often splits during the run, on the one hand because in the case of compression a ridge forms which extends as far as the printing surface and causes alternation of load, and on the other hand, because relatively thin printing plates are very easily over-stretched.

The purpose of the invention is to clamp the printing plates in true register. Particularly, in the case of multicolor printing, the printing plates should be adjustable or deformable by means of the clamping rails on the tail end so that the subsequent colors are applied true to register in spite of alteration of the print images.

A principal object of the invention is to permit deformation of the printing plate at the tail end without splitting of the printing plate occurring during the run.

Another object of the invention is to provide new and improved clamping means for printing plates.

Another object of the invention is to provide new and improved clamping means for printing plates having clamping rails for the plate, said rails being adjustable axially and sideways.

Another object of the invention is to provide new and improved clamping means for printing plates having means to apply tension to the printing plates.

The present invention consists of the top clamping rail of a clamping rail pair overlapping the bottom clamping rail of the adjacent clamping rail pair and in the overlapping clamping rail ends being lockable to one another by means of at least one clamping screw passed through slots.

The advantage of overlapping arrangement of the clamping rail pairs is that the range of extension is considerably greater than in the case of the known clamping devices as the clamping screws in the area of overlap are released during deformation of the rear edge of the printing plate. During compression no ridge can form because the overlapping clamping rail ends are applied again for clamping the printing plate ends after deformation.

The above mentioned causes of tearing of printing plates are thus eliminated. In addition, the invention provides the advantage that both pairs of clamping rails are axially adjustable in the same way as a single clamping rail pair as a result of the connection of two overlapped clamping rail ends.

Other features which are considered as characteristic of the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in a particular embodiment, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which: 1

FIG. 1 is a plan view of a cylinder with aplate clamping device in accordance with the invention,

FIG. 2 is a longitudinal section through the cylinder of FIG. 1, and

FIG. 3 is a cross-section through the same cylinder at lines 33 of FIG. 1.

Cylinder 1 has, between the two cylinder end flanges 2 and 3 having the form of a bearer ring a slot or passage 4 in which the clamping device for printing plate 5 is accommodated in the usual way. The plate leading end 6 of the printing plate 5 is held in position by a continuous pair of clamping rails which consists of the bottom clamping rail 7 and the top clamping rail 8. Both clamping rails 7 and 8 are joined together by clamping screws 9. Tightening the clamping screws 9 against the pressure of compression springs 12, causes clamping of the plate end 6 by means of the clamping faces 10 and 1 l The bottom clamping rail 7 is movably located in slot passage 4 and is adjustable in axial direction of the form cylinder by means of adjusting screws 13 and at right angle thereto in slot passage 4 by means of tensioning screws 14.

To hold donw the bottom clamping rails there are fitted transversely in passage 4 two T-shaped hold-down screw assemblies 15 which are inserted in suitably shaped slots 16 in the bottom clamping rails. The size of the slots 16 is such that axial movement of the pairs of rails is possible by screws 13.

At its tail end, plate 5 is held in position by two pairs of clamping rails mounted behind one another in axial direction of form cylinder 1. One pair of clamping rails has a bottom clamping rail 17 projecting past the machine center 24 and a considerably shorter top clamping rail 18. The other pair of clamping rails consist of a shorter bottom clamping rail 19 and a top clamping rail 20 projecting past the machine center 24. Thus, the bottom clamping rail 17 of one clamping rail pair 17 and 18 is overlapped by the top clamping rail 20 of the other clamping rail pair 19 and 20. The two overlapping clamping rail ends are joined together by two clamping screws 9'. In contrast to the other clamping screws 9 of the two clamping rail pairs I7, 18 and 19, 20 these screws 9 are located in slots 21. The overlapping clamping rail ends can thus be moved in relation to one another. If the two center clamping screws 9' are tightened, the two clamping rail pairs l7, l8 and 19, 20, form one unit and can be adjusted together by means of the outer adjusting screws 13 in axial direction of the cylinder 1 or by means of the tensioning screws 14 in direction of tension. Each of the two bottom clamping rails 17 and 19 has a slot 16 into which a hold-down projects in each case.

By tightening all clamping screws 9, 9' of both clamping rail pairs 17, 18 and 19, 20, the rear plate end is clamped. Only now can tensioning be carried out by turning the tensioning screws.

Between the two top clamping rails 18 and 20 a central adjusting screw 23 is provided by means of which the two clamping rail pairs 17, 18 and 19, 20, can be moved away from one another by slackening the two center clamping screws 9' or moved closer to one another with the aid of the two outer adjusting screws.

If the machine operator establishes during multicolor printing that one of the printing plates 5 is not printing true to register, that is to say, applies the print image wider or narrower, he can correct this fault with the aid of the invention by slackening the two central clamping screws 9' and adjusting the three adjusting screws 13 and 23 in such a way that according to the nature of the deviation, whether printing is narrower or wider, the center section of the printing plate end can be compressed or extended. The deformation section is then at least as large as the overlap of the clamping rails. Ridge formation in the center plate section or excessive extension is thus prevented. After deformation of the printing plate end, to restore true to register condition the central clamping screws 9',are retightened.

We claim:

1. ln means for clamping printing plates onto cylinders of offset printing presses, the cylinders having end flanges and an axially extending slot along said cylinders between said end flanges, a clamping assembly positioned in said slot, said clamping assembly comprising, two or more tandem mounted clamping rail pairs, each of said rair pairs consisting of a top and a bottom clamping rail and slots positioned in said top clamping rail, clamping screws for clamping the printing plate between and in contact with the top and bottom clamping rail pairs, screws for circumferentially tensioning the printing plate on said cylinder, screws for axially adjusting and supporting said clamping rail pairs rela tive to one another and to the end flanges, means to avoid ridges in a plate while deforming said plate by providing that said tandem mounted clamping rail pairs are mounted in said axially extending slot in such a manner that said top clamping rail overlaps said bottom clamping rail of an adjacent rail pair, and means to clamp overlapping rail ends together comprising at least one clamping screw passing through said slots in said top clamping rail, whereby said overlapping rail ends may be released during deformation of said plate to greatly increase the said deformed area of said plate.

2. Apparatus as in claim 1 wherein said screws for axially adjusting said clamping rail pairs provide common axial displacement of said clamping rail pairs. 

1. In means for clamping printing plates onto cylinders of offset printing presses, the cylinders having end flanges and an axially extending slot along said cylinders between said end flanges, a clamping assembly positioned in said slot, said clamping assembly comprising, two or more tandem mounted clamping rail pairs, each of said rair pairs consisting of a top and a bottom clamping rail and slots positioned in said top clamping rail, clamping screws for clamping the printing plate between and in contact with the top and bottom clamping rail pairs, screws for circumferentially tensioning the printing plate on said cylinder, screws for axially adjusting and supporting said clamping rail pairs relative to one another and to the end flanges, means to avoid ridges in a plate while deforming said plate by providing that said tandem mounted clamping rail pairs are mounted in said axially extending slot in such a manner that said top clamping rail overlaps said bottom clamping rail of an adjacent rail pair, and means to clamp overlapping rail ends together comprising at least one clamping screw passing through said slots in said top clamping rail, whereby said overlapping rail ends may be released during deformation of said plate to greatly increase the said deformed area of said plate.
 2. Apparatus as in claim 1 wherein said screws for axially adjusting said clamping rail pairs provide common axial displacement of said clamping rail pairs. 